Hawks spokesperson Brig Hangwani Mulaudzi said the four would remain in custody until they return to court on January 21.

"Their arrest follows investigations by the Hawks’ serious organised crime investigation [unit] and Crime Intelligence. Various firearms and 5,300 ammunition of different calibres, documents and other items were confiscated by the Criminal Record Centre (CRC) for further probing," said Mulaudzi.

Heymans and the Abrams brothers were arrested on Friday.

Knoesen, who was arrested on Thursday, is a retired pastor and former SANDF member. He is alleged to be the head of the National Christian Resistance Movement, a right-wing organisation also known as the Crusaders.

Their arrests followed a two-year intelligence-led investigation into an alleged terrorist plot apparently co-ordinated by the group. The plot allegedly planned to target national keypoints, shopping malls and informal settlements.